1. Field of the Invention
The present invention relates to the field of insulation technology for windings of electric machines.
Stator winding insulation of the type initially mentioned comprises a mica band with at least one layer-like carrier and with a mica layer fixed to at least one face of the carrier with the aid of a binder. Stator winding insulation of this type is used preferably in windings of electric machines for high powers and utilization.
2. Discussion of Background
The present invention refers to a state of the art of winding insulations such as is described, for example, in H. Sequenz: Herstellung elektrischer Wicklungen [Manufacture of electric windings], Springer Verlag, 1973, especially pages 62 and 63. In the sequenz article, winding insulations of this type comprise mica bands which contain fibrous solid sheets, such as paper, silk or glass textile fabric, to which one or more plies of laminated mica or mica paper are adhesively bonded by means of a flexible binder. The insulating properties of winding insulation composed of such mica bands are determined primarily by the dielectrically high-grade mica and by the dielectrically lower-grade materials of the carrier and of the binder or impregnating agent.
A critical factor in insulating the stator winding conductors of electric machines relative to the grounded lamination bundle is electric and mechanical properties of the main insulation. In the case of rated voltages of some 100 V up to 30000 V, the thickness of the main insulation varies within the range of 0.5 to 8 mm in the case of a stress of approximately 2 kV/mm. In addition to this, there is the high demand placed on the insulation, this being the result of thermal stress and, in the case of machines with long stator core lengths, of thermal mechanical expansion forces in the longitudinal direction of the slot.